Rack and Pinion Driven Gas Compressor

ABSTRACT

A gas compressor is provided. The gas compressor comprises a motor, a pinion operatively coupled to the motor, a rack gear driven by the pinion, at least one inlet gas connection and at least one outlet gas connection, and a piston and piston rod reciprocal within a compressor cylinder. The piston rod is coupled to the rack gear, whereby gas entering the compressor cylinder through the at least one inlet gas connection is compressible within the cylinder by the piston and dischargeable from the cylinder through the at least one outlet gas connection. A method of compressing gas is also provided and comprises the steps of operating a motor coupled to a rack and pinion system, wherein the rack and pinion system is coupled to a piston and piston rod within a compressor cylinder.

FIELD OF THE INVENTION

This invention is in the field of compressors, and more specifically to gas compressors.

BACKGROUND

During oil production, gas can accumulate in the casing lining the production well, restricting the flow of hydrocarbon from a formation into the production well and causing gas locking of the down hole pump.

If casing pressure is high in relation to the formation pressure, free gas will enter the pump barrel. Due to compression of the gas, sufficient pressure can build in the pump barrel to prevent opening of the valves, resulting in these gas locks. Additionally, this gas back-pressure in the hydrocarbon well's annulus can generate a restriction to oil and gas flow from the formation into the well bore. These issues can mean that little or nothing is pumped, thus reducing pump volumetric efficiency and hydrocarbon production.

If the casing pressure in wells with low formation pressure can be reduced, gas volumes that enter the pump barrel can be minimized and hydrocarbon may more readily flow from the surrounding formation into the production well. This can also ease the gas lock problems and overall increase well production.

Gas compressors have long been used as a solution to decrease the gas-back pressure in well casings by capturing and compressing the vented gas into a sales line or flow line. Gas compressors act to draw gas from the casing side of a well and discharge the gas into the flow line, which is a tube connected to the annulus. This reduces gas back-pressure downhole and on the formation face, allowing additional oil to enter the well bore and to flow out of the formation, thus relieving the flow in the oil and gas delivery line. It can additionally minimize gas entry into the pump barrel, preventing gas locks.

Conventional cylinder style gas compressors are mounted on a pump jack and are driven by the walking beam of the pumping unit. As these piston style gas compressors are mounted on a pump jack and driven by the walking beam, they are often referred to as walking beam compressors. The action of the walking beam is used as the prime mover for these compressors.

Compressors that are driven by pump jacks are typically designed to be specific to the producer and well, and will be chosen or designed according to considerations such as (but not limited to) gas flow, well casing pressure, oil delivery line pressure, pump jack model, sucker rod stroke, double strokes per minute, and the working schedule of the pump jack. Its capacity is oftentimes entirely dependent on the number of double strokes per minute of the pump jack and the function-pause schedule of the well pump jack. This means that the functioning and efficiency of the compressor is dependent on the operation of the pump jack. As such, the compressor design, operation, and maintenance will be largely dictated by the pump jack used.

Additionally, installation of the compressor on the pump jack results in downtime of the pump jack, meaning that production must halt while the compressor is being installed. Installation can take from a few days to several days, which can stall production and result in much wasted time. Furthermore, when the compressor is misapplied or installed incorrectly, or when the compressor simply malfunctions in any way, this can cause problems for the entire operation, resulting in further wasted time and money and loss of pump jack warranty.

It would be advantageous to have a gas compressor that allows for increased production and smoother well operation.

SUMMARY OF THE INVENTION

It would be advantageous to have gas compressor that allows for efficient and smooth well operation, regardless of the activity of a pump jack unit operating on the same production well.

In an aspect, a gas compressor driven by a rack and pinion drive system is provided. The gas compressor has a piston and piston rod reciprocal within a compressor cylinder. The piston rod is operatively coupled to a rack gear, which is driven by a pinion that is operatively coupled to a motor.

In a further aspect, a method of compressing gas comprises the step of driving a piston and piston rod within a compressor cylinder by operating a motor coupled to a rack and pinion system, which in turn, is coupled to the piston rod.

The gas compressor and method of using the gas compressor can allow for recovery of vapours from on-site processing and storage equipment, as well as decrease gas locking and compress methane gas from surface casing vents into a flow line, without significantly disrupting or hindering well production operation due to maintenance or repair. The free gas can be diverted into the annulus and can be produced.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagram, and where:

FIG. 1 is a side cross-sectional view of gas compressor in an aspect of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

A gas compressor driven by a rack and pinion drive system is provided. The gas compressor can be used in oil production systems and can operate independently of a pump jack and other surrounding equipment, and in this way, can be optimized for its best performance, regardless of the operation and specifications of other equipment. It can also be repaired or replaced independently of other equipment, so its repair or maintenance does not halt or hinder operations.

FIG. 1 illustrates a gas compressor 10 in an aspect of the present invention. The gas compressor 10 shown is a cylinder or piston-style compressor and is driven by a rack and pinion drive system 20. The compressor 10 could be used in various fields of endeavor and adapted for various uses, including for moving gas from a wellhead or casing or a production well into a gas sales line.

The compressor 10 has a piston rod 12 having a first end 21 and a second end 22. The first end 21 is operatively connected to a piston 13 and the second end 22 is coupled to the rack and pinion drive system 20. A cylinder 14 is provided within which the piston rod 12 and piston 13 can reciprocate. Also provided is at least one inlet or suction gas connection and at least one outlet or discharge gas connection 18, 19. In the aspect shown in FIG. 1, the inlet and outlets 18, 19 operate to both suction gas inward as well as discharge gas outward, and could operate automatically by, for example, detecting differential pressures, or they could be manually operated. However, in other aspects of the invention, there may be inlets that act as suction gas connections that are separate and operate independently of outlets acting as discharge gas connections.

The compressor piston 13 is driven by the rack and pinion drive system 20 with the rack and pinion system 20 being used as the prime mover for operating the compressor 10. The rack and pinion drive mechanism 20 has a rack gear 32 and a rotating pinion 34 that meshes with or otherwise engages the rack gear 32. The second end 22 of the piston rod 12 is coupled to the rack gear 32, which reciprocates linearly through rotational motion of the pinion 34, which in turn, is driven by a motor 36. The rack and pinion system 20 in this way converts rotational movement provided by the motor 36 coupled to the pinion 34 into reciprocating linear movement of the rack gear 32, and thus, the piston rod 12 and piston 13.

The rack and pinion system 20 shown has a linear rack gear 32, though any type of rack and pinion system could be used in this system, including an endless arcuate rack gear with corresponding pinion, or a circular rack gear. A curved rack gear could also be used, or any other rack and pinion arrangement that will allow the maintenance of the pinion in stable engagement with the rack gear.

The motor 36 can be manufactured to be integral with the compressor 10, or can be removable therefrom. Many types of motors could be used to drive the compressor 10 so as to impart reciprocal movement of the piston rod 12 and piston 13 within the cylinder 14, and could depend on the type of rack and pinion system 20 used. In an aspect, the motor 36 is a reversing electric motor that drives the pinion 34 in alternate clockwise and counterclockwise directions, thus moving the rack gear 32 linearly forward and backward and in turn imparting the necessary reciprocal motion to the piston rod 12 and piston 13. An electronic device could be used for control of the motor 36. In some aspects of the invention, a variable frequency drive (VFD) to allow for speed adjustments can be provided. Such speed adjustments could operate through open- or closed-loop control of the compressor 10. For example, pressure readings could be provided by a sensor, which would signal an increase in the speed of the motor 36 and thus the operation of the compressor 10 during lower pressure readings in the cylinder 14. As the pressure in the cylinder 14 increases to a point at or near the pressure capacity of the cylinder 14, the speed of the motor 36 and thus the cylinder 14 could be slowed. As a further example, control of the speed of the compressor 10 could be based on position of the piston 13 or piston rod 12 during the compressor 10 stroke, rather than using pressure readings. A programmable logic controller could be provided that would give instructions to slow or quicken the compressor 10 at predetermined positions of the compressor 10 stroke. Other examples of such speed control would be to use load readings or amp readings to adjust speed of the compressor 10 to efficiently operate the compressor 10, while remaining within the compressor 10's capacity to handle the load.

In the compressor 10 of FIG. 1, the compressor 10 is a reciprocating or piston compressor with the compressor 10 having a piston rod 12 operatively driven by the motor 36. The piston rod 12 is connected to the piston 13 contained in the cylinder 14. The piston 13 acting within the cylinder 14 can compress gas contained within the cylinder 14. As gas enters the cylinder 14 through a suction valve 18, 19 at suction pressure, it can be compressed to reach a desired discharge pressure. Once the desired discharge pressure has been reached, the gas can be discharged through a discharge valve 18, 19. The discharged gas can then be diverted into a flow line and produced.

The compressor 10 could be any type of piston-style compressor, including a single action or dual action compressor. Depending on the system design and type of compressor, the cylinder may have one or multiple suction and discharge valves. In an aspect, the compressor 10 is a double acting compressor whereby during the piston rod 12 up stroke, gas is pulled from the casing into a bottom chamber 40 of the compressor cylinder 14 through a suction check valve 18, 19 in communication with the bottom chamber 40. Simultaneously, gas is compressed from the top chamber 42 through a discharge check valve 18, 19 in communication with the top chamber 42 and into the flow line. During the piston rod 12 down stroke, gas is pulled from the casing and into the top chamber 42 through a second suction check valve 18, 19 and simultaneously gas is also being compressed from the bottom chamber 40 through a second discharge check valve 18, 19 and into the flow line.

It is contemplated that the cylinder 14 can be sized to accommodate any pressure or capacity, depending on the compressor 10's use. The size of the gas compressor 10 can vary, but since it is not dependent on other machinery or equipment, such as a pump jack's operation, the size can independently be configured to compress the daily gas production at the operator's desired casing pressure, as needed. The cylinder 14, piston rod 12, and piston 13 could be constructed out of corrosion-resistant materials to protect against corrosive materials which might be found, for example, in natural gas.

The rack and pinion arrangement 20 and/or the compressor 10 can be made to be mobile or portable, to be moved to locations, for example, other oil production wells, with minimal cost. For example, the arrangement 20 and/or the compressor 10 can be built on a skid so at to allow the arrangement 20 and/or compressor 10 to be picked up, or otherwise it may be mounted on a trailer, to be moved. Various devices can be used for attachment and detachment of the compressor cylinder 14 and/or rack and pinion system 20 to the well casing or any other equipment upon which the compressor 10 or system 20 may be mounted. In an aspect, the compressor 10 could be connected to the gas source such as a wellhead annulus and sales or flow line with a pressure rated hose, which would allow for quicker installation and portability, or the compressor 10 could be pipe-fitted in, allowing for a more permanent installation.

While the use of the rack and pinion drive system 20 to drive a compressor 10 is not limited to the field of oil and gas, the rack and pinion arrangement 20 can be used for casing gas compression and/or removing compressed gas from oilfield tank systems.

By driving the compressor 10 with the rack and pinion system 20, the compressor 10 no longer needs to be mounted on a pump jack walking beam. The system 20 can be used with and installed on any type of pumping equipment unit, including screw pumps, electric submersible pumps, as well as any type of pump jack including a Rotaflex™ pumping unit. By not having to mount to the pump jack, the compressor unit 10 can be easily moved from location to location, as required.

By utilizing the rack and pinion drive system 20, the volume of the compressor 10 is no longer limited by the speed of a pump jack or by the amount of time per day the pump jack is actually in operation. By not having the system 20 mounted on the pump jack, warranty issues from the pump jack manufacturers are eliminated as well as possible damages to the pump jack by the mounting and operation of a beam driven gas compressor. By utilizing the piston style gas compressor 10, the system can provide the flexibility of a skid mount compressor package, along with the low maintenance, simple design of a beam compressor.

While FIG. 1 only shows a rack and pinion drive mechanism 20 mounted on a piston type gas compressor 10 and driven by a reversing electric motor 36, it is contemplated that other equipment can be provided on or with the compressor system 10. For example, some aspects of the invention may incorporate a pressure sensing system to provide control for starting, stopping, and speed control. Other equipment that may be provided in some aspects of the invention include a liquid separator or scrubber for gas entering the gas compressor 10, which can be installed on the gas line from the well casing to the compressor 10. These separators can remove entrained particulates, moisture, and liquid process fluid that could cause damage to the compressor valves 18, 19. A pressure regulator could be provided to provide a minimum required by the pressure in the well casing, and a gas flow meter or counter for the flow pumped from the well casing. In an aspect, an electronic temperature monitoring and automatic overheating protection system is included and/or a pressure safety valve could also be included.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention. 

1. A gas compressor comprising: a motor; a pinion operatively coupled to the motor; a rack gear driven by the pinion; at least one inlet gas connection and at least one outlet gas connection; and a piston and piston rod reciprocal within a compressor cylinder, the piston rod being coupled to the rack gear, whereby gas entering the compressor cylinder through the at least one inlet gas connection is compressible within the cylinder by the piston and dischargeable from the cylinder through the at least one outlet gas connection.
 2. The gas compressor of claim 1 wherein the compressible gas comprises methane from at least one of a wellhead, a casing, and a production line.
 3. The gas compressor of claim 2 further comprising a gas sales line.
 4. The gas compressor of claim 1 wherein at least one of the at least one inlet and at least one of the at least one outlet comprise one and the same gas connection.
 5. The gas compressor of claim 4 wherein the one and the same gas connection operates automatically by detecting differential pressures.
 6. The gas compressor of claim 1 wherein the rack gear is linear.
 7. The gas compressor of claim 1 wherein the motor is removable.
 8. The gas compressor of claim 1 wherein the motor is a reversing electric motor.
 9. The gas compressor of claim 1 further comprising a variable frequency drive.
 10. The gas compressor of claim 9 wherein the variable frequency drive allows for an increase in speed of the compressor when pressure in the cylinder is lower than a predetermined pressure point, and a decrease in speed of the compressor when pressure in the cylinder is higher than a predetermined pressure point.
 11. The gas compressor of claim 1 wherein the gas compressor is a dual action compressor.
 12. The gas compressor of claim 1 further comprising pressure rated hoses for removably connecting the gas compressor to a gas source.
 13. The gas compressor of claim 1 wherein the compressor is pipe-fitted in to a gas source.
 14. The gas compressor of claim 1 wherein the compressor is portable to and from a gas source.
 15. A method of compressing gas comprising the steps of: operating a motor coupled to a rack and pinion system, wherein the rack and pinion system is coupled to a piston and piston rod within a compressor cylinder.
 16. The method of claim 15 further comprising the step of venting the compressed gas into a gas sales line.
 17. The method of claim 15 further comprising the step of capturing methane in the compressor cylinder from at least one of a wellhead, a casing, and a production line.
 18. The method of claim 15 further comprising the step of operating a variable frequency drive.
 19. The method of claim 18 further comprising the step of increasing the speed of the compressor when pressure in the cylinder is lower than a predetermined pressure point, and decreasing the speed of the compressor when pressure in the cylinder is higher than a predetermined pressure point. 